It looks like Lowrance has posted the HDS Gen2 Touch 5.5 and HDS Gen3 3.5 update files on their website.

This Software update will give the following features:
• Use of the TotalScan Skimmer Transducer ‐ HDS Gen 3 only
– TotalScan Skimmer Transducer scheduled to start shipping March 2016
• Support for the Precision‐9 compass – Gen2 Touch and Gen 3
• WM‐3 SiriusXM® Local Weather Support
• Network Analyzer and Service Assistant feature improvements
• Jeppesen C‐MAP performance improvements
• Bug Fixes and Software Improvements

Bug Fixes and Improvements
• Radar PPI can now show 6 range rings instead of the default 4 range rings (toggle
on in Settings > System > Advanced
• Improved color and contrast for StructureScan 3D Leading Edge™
• Improved speed for device upgrades over the NMEA 2000® network – up to 4x
faster
• Fixed a bug where the data overlay settings were not saved after making changes
• Fixed a bug where Global and Local network settings changes were not retained
after a power cycle of the unit
• Fixed a bug that allowed for the “Halo Light” option to be viewed in HDS
Gen2T/Gen3 simulators – Halo radar is not compatible with HDS